The invention is directed to a sheet film magazine for a film changer comprising a conveyor means for conveying individual sheets of film from a film stack to the exposure portions of the film changer. The conveyor means comprises at least one conveyor wheel which is attached to a shaft parallel to the plane of the sheets of film and which is driven in the conveying direction of the sheets of film with drive means. The conveyor means also comprises means that vary the spacing between a sheet of film and the conveyor wheel such that the conveyor wheel, when conveying a sheet of film from the sheet film magazine to the exposure portion, presses against the surface of the sheet of film and is removed from the surface of the sheet of film after the film conveying has ended.
A sheet film magazine of this type that is not provided for a film changer is disclosed by German Published Application 2 747 623. The conveyor means of the sheet film magazine comprises a pressure plate which is secured to the one end of an arm that proceeds along nearly the entire loading part of the magazine and whose other end is seated rotatably around an axis. The pressure plate together with the arm are arranged above the film stack or the sheet of film. A conveyor wheel is attached under the film stack. When conveying a sheet of film from the sheet film magazine, the arm together with the pressure plate is pivoted down against the end of the film stack which lies above the conveyor wheel. When the pressure plate presses against the film stack, the latter is pressed against the conveyor wheel, as a result whereof the undermost sheet of film of the film stack can be conveyed. Subsequently, the pressure plate is lifted up with the assistance of two supporting arms that proceed in parallel. The one end of each supporting arm runs on a rail which is attached to the floor of the magazine. The other ends of the supporting arms each respectively carry a roller that presses against the arm of the pressure plate. The supporting arms are thus displaceable along the entire length of the pressure plate arm. When the pressure plate presses against the film stack, the supporting arms together with the rollers are situated in the region of the axis around which the arm is turned. When a sheet of film has been conveyed out of the magazine, the supporting arms are displaced in the direction of the pressure plate, whereby the pressure plate lifts off from the film stack. When conveying the next sheet of film, the supporting arms are displaced in the direction of the axis around which the pressure plate arm can be turned, whereby the pressure plate again presses against the film stack. The relatively complicated and long-distanced displacement of the supporting arms for controlling the motions of the pressure plate that has just been described is time-consuming, so that a high film conveying frequency required in a film changer is not possible with this conveyor means.
U.S. Pat. No. 3,234,796 discloses an x-ray film changer having a conveyor means for conveying sheets of film from the exposure part to the reception cassette. The conveyor means which is attached in front of the film entry opening of the reception cassette contains a conveyor wheel and a pressure roller. The pressure roller can be brought into a first position in which it presses against the conveyor wheel and can be brought into a further position in which it is arranged at a distance from the conveyor wheel. The pressure roller is secured to an end of a lever arm at whose other end a control roller is arranged, this control roller running under spring pressure on a cam plate that is provided with two cams. When the cam plate has a position wherein the control roller lies against the cam, the lever arm is turned around a shaft such that the pressure roller presses against the conveyor wheel. When the cam plate is subsequently turned into a position between the cams, the lever arm is turned around its axis such that the pressure roller lifts off from the conveyor wheel. The control of the pressure roller is dependent on the length of the cams, this meaning that the control roller must run along the entire cam length before the pressure roller lifts off from the conveyor wheel. This can prevent a high film conveying frequency.